1. Technical Field
This invention relates to electrostatographic reproduction apparatus which produce transferable toner images on a movable dielectric member. More particularly, this invention relates to such a reproduction apparatus having an endless web dielectric member and a adjustable detack roller assembly.
2. Background Art
Electrostatographic reproduction apparatus are well known which each have an imaging member such as an endless dielectric rigid drum or flexible web member. Each also includes subsystems for forming transferrable toner images on the dielectric member, and a subsystem for transferring the toner images to a copy sheet that is fed into intimate and image-transfer relation with the dielectric member. Each copy sheet after receiving the transferred image is separated or stripped from the dielectric member for subsequent fusing of the toner images on the copy sheet.
As disclosed for example in U.S. Pat. No. 4,410,262, issued Oct. 18, 1983 to Ariyama et al, the process of separating or stripping a copy sheet from the dielectric member (just after toner images have been transferred to the copy sheet) is critical and can result in image defects if not handled properly. Where the dielectric member is a rigid drum, it is known, as discussed in the Ariyama et al patent (above), to use sheet-stripping fingers, or sheet pick-off belts to separate the copy sheet from the rigid drum. Where the dielectric member is a flexible web or belt, it is known to train a portion of the web over what is referred to as a "detack roller" (at the point where copy sheets are to be separated or stripped from the web).
The use of a "detack roller" to strip copy sheets as such presents a set of conflicting objectives and problems. Separating a copy sheet using a detack roller relies in great part on the beam strength of the copy sheet. The process essentially entails moving both the copy sheet and flexible web about the detack roller such that the web alone is wrapped around the detack roller with the expectation that the copy sheet (because of its beam strength) will remain in a tangential path to the detack roller. The copy sheet will thus be forced to separate at a particular separation angle from the web. As such, the larger the separation angle, the sharper it is, and the easier the separation of the sheet from the web, even for lightweight, low-beam strength copy sheets. Therefore, reducing the size or diameter of the detack roller improves such separation because it increases the sharpness of the sheet separation angle.
Unfortunately, however, decreasing the size or diameter of the detack roller as such undesirably tends to result in a bending or "core-setting" of the flexible web during periods when the reproduction apparatus is idle with the flexible web wrapped around such a small diameter roller. Such undesirable bending or core-setting can result in subsequent image formation defects as well as in early failure or deterioration of the web itself.